Semiconductor device and manufacturing method thereof

ABSTRACT

A semiconductor substrate has a trench in a first main surface. An insulated gate field effect part includes a gate electrode formed in the first main surface. A potential fixing electrode fills the trench and has an expanding part expanding on the first main surface so that a width thereof is larger than the width of the trench. An emitter electrode is formed on the first main surface and insulated from the gate electrode electrically and connected to a whole upper surface of the expanding part of the potential fixing electrode. Thus, a semiconductor device capable of enhancing reliability in order to prevent an aluminum spike from generating and a manufacturing method thereof can be provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and amanufacturing method thereof.

2. Description of the Background Art

As a power semiconductor device as a switching element for driving amotor and the like, an IGBT (Insulated Gate Bipolar Transistor) ismainly used in a region where a regular voltage is 300V or more.

As such a power semiconductor device, a constitution, in which two typesof trench inside IGBT cells are provided for both a gate-trench and anon-gate trench filled with a conducting material directly connected toan emitter electrode to have the same potential of emitter region not agate, has been conventionally proposed (refer to Japanese PatentLaying-Open No. 2002-353456, and Pamphlet of International PublicationNo. WO 02/058160).

Especially, according to the Japanese Patent Laying-Open No.2002-353456, the gate electrode of the IGBT and the filling layer havingthe emitter potential are formed in the same step.

According to the manufacturing process, a trench for the gate electrodeand a trench for the filling layer are first formed in a substrate, anda first insulation film is formed so as to cover an inner wall of eachof the trenches. Then, a conductive layer is formed on a whole surfaceof the substrate so as to fill the trenches, and the conductive layer isfully etched away. Thus, the conductive layer remains only in each ofthe trenches, whereby the gate electrode and the filling layer areformed.

Then, a second insulation film is formed on a whole surface of thesubstrate so as to cover the gate electrode and the filling layer, andthe second insulation film is selectively etched away. Thus, a contacthole exposing the periphery of the filling layer is formed on the secondinsulation film, and the second insulation film on the gate electroderemains. Thereafter, when an emitter electrode is formed on a wholesurface, the emitter electrode is electrically connected to the fillinglayer through the contact hole, and electrically insulated from the gateelectrode by the second insulation film.

Thus, the gate electrode of the IGBT and the filling layer having theemitter potential are formed in the same step.

However, according to the constitution and manufacturing methoddisclosed in the Japanese Patent Laying-Open No. 2002-353456, a fine gapis generated between the filling layer and the trench inner wall, and analuminum spike is generated at that part, which lowers the reliability.This will be described hereinafter.

According to the manufacturing method disclosed in the Japanese PatentLaying-Open No. 2002-353456, several tens % of the thickness of thesecond insulation film is processed by overetching in general in theetching process for forming the contact hole. This overetching isperformed in view of the variation in thickness of the second insulationfilm on a wafer surface and between wafer surfaces and variation inetching speed of an etching equipment.

A predetermined amount of the first insulation film formed between thefilling layer and the inner wall surface of the trench is etched away bythis overetching. Thus, an extremely small gap as much as the thicknessof a gate oxide film is generated between the filling layer and theinner wall surface of the trench.

In addition, before a high melting point metal to form silicide bycontact with silicon is formed by sputtering or the like, the surface isetched with fluorinated acid (HF) in order to remove a natural oxidefilm of the exposed part of silicon in addition to general cleaning ofthe contact hole part using acid or alkaline fluid. Also at this time ofetching, a predetermined amount of the first insulation film formedbetween the filling layer and the inner wall surface of the trench isetched away. Thus, the first insulation film between the filling layerand the inner wall surface of the trench is further deeply etched away.

The gap generated as described above is as fine as a processingdimension of the most advanced LSI (Large Scale Integrated Circuit) andhas a sectional structure that can be regarded as a double contact holegenerated in the contact hole. Therefore, even when a sputteringapparatus used for the most advanced LSI is used, it is extremelydifficult to fill this gap with a metal film such as titanium (Ti) filmas a barrier layer. Even when a metal film is put on the gap, it isinevitable that the film is thinned and a pinhole is generated.

As a result, aluminum as an emitter electrode material and silicon as asubstrate material are directly reacted through the metal film having alow barrier property by a heat treatment in the following step orelectro migration reaction generated when a current is applied for anormal element operation. Thus, silicon is diffused in aluminum, and atthe same time, aluminum eats away in the silicon as a spike (that is, analuminum spike is generated), so that the electric characteristics areconsiderably damaged and long-term reliability cannot be maintained.

SUMMARY OF THE INVENTION

The present invention was made in view of the above problem, and it isan object of the present invention to provide a semiconductor devicecapable of enhancing reliability in order to prevent an aluminum spikefrom generating, and a manufacturing method thereof.

A semiconductor device according to the present invention includes asemiconductor substrate, an element, a potential fixing electrode, andfirst main electrodes. The semiconductor substrate has a first mainsurface and a trench in the first main surface. The element has aninsulated gate field effect part including a gate electrode formed inthe first main surface. The potential fixing electrode fills the trenchand has an expanding part on the first main surface so that a widththereof is larger than that of the trench. The first main electrodes areformed on the first main surface, electrically insulated from the gateelectrode, and connected to a whole upper surface of the expanding partof the potential fixing electrode.

A manufacturing method of a semiconductor device according to thepresent invention includes the following steps.

A trench is formed in a main surface of a semiconductor substrate. Aconductive layer is formed on the main surface so as to fill the trench.A potential fixing electrode filling the trench and having an expandingpart expanding on the main surface so that a width thereof is largerthan that of the trench is formed and a gate electrode is formed on themain surface by patterning the conductive layer. Insulation layers areformed so as to cover the gate electrode and expose the expanding partof the potential fixing electrode. Main electrodes are formed so as tobe electrically insulated from the gate electrode and connected to awhole upper surface of the expanding part of the potential fixingelectrode.

According to the present invention, since the potential fixing electrodeexpands on the first main surface so that a width thereof is larger thanthe trench width, a gap is prevented from being generated between thepotential fixing electrode and the wall surface of the trench. Thus, ahighly reliable semiconductor device can be provided.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view schematically showing the constitution of asemiconductor device according to Embodiment 1 of the present invention;

FIGS. 2 to 11 are schematic sectional view showing a manufacturingmethod of the semiconductor device according to Embodiment 1 of thepresent invention step by step;

FIG. 12 is a schematic sectional view showing a state where a gap isgenerated between potential fixing electrode 12 b and the inner wallsurface of trench 1 b;

FIG. 13 is a sectional view schematically showing the constitution whenthe constitution shown in FIG. 1 is applied to a vertical PT type IGBT;

FIG. 14 is a sectional view schematically showing the constitution whenthe constitution shown in FIG. 1 is applied to a vertical LPT type IGBT;

FIG. 15 is a sectional view schematically showing the constitution whenthe constitution shown in FIG. 1 is applied to a vertical NPT type IGBT;

FIG. 16 is a sectional view schematically showing the constitution whenthe constitution shown in FIG. 1 is applied to a vertical MOSFET;

FIG. 17 is a sectional view schematically showing the constitution whenthe constitution shown in FIG. 1 is applied to a lateral IGBT;

FIG. 18 is a sectional view schematically showing the constitution of asemiconductor device having a planar gate structure according toEmbodiment 3 of the present invention;

FIG. 19 is a sectional view schematically showing the constitution of acarrier storage type IGBT as a semiconductor device according toEmbodiment 4 of the present invention;

FIG. 20 is a sectional view schematically showing the constitution of aMCT as a semiconductor device according to Embodiment 4 of the presentinvention;

FIG. 21 is a sectional view schematically showing the constitution of anIEGT as a semiconductor device according to Embodiment 4 of the presentinvention;

FIG. 22A is a schematic plan view showing an example in which the shapeof an emitter region is changed and showing a state where an emitterelectrode and the emitter region are electrically connected; and

FIG. 22B is a schematic sectional view taken along a line XXIIB-XXIIB inFIG. 22A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described with reference tothe drawings hereinafter.

Embodiment 1

With reference to FIG. 1, a semiconductor device according to thepresent embodiment can be applied to a vertical or lateral MOSFET (MetalOxide Semiconductor Field Effect Transistor), an IGBT and the like.

Description will be made taking as an example the constitution of an MOSgate part on a surface of the IGBT or MOSFET having a trench gatestructure. While an n-channel MOS gate will be taken as an example forconvenience of the description, the constitution and effect are the samewith the MOS gate of an opposite conductivity type, that is, a p-channeltype.

For example, an n⁻ region 2 serving as a drift region is formed in asemiconductor substrate 1 formed of silicon. A p-type region 3 servingas a base region, for example, is formed on n⁻ region 2 on the firstmain surface side of semiconductor substrate 1. An n-type region 4serving as an emitter region (source region) is selectively formed inp-type region 3 on the first main surface side of semiconductorsubstrate 1.

A trench 1 a is formed in the first main surface of semiconductorsubstrate 1 so as to penetrate n-type region 4 and p-type region 3 andreach n⁻ region 2. In addition, a trench 1 b is formed in the first mainsurface of semiconductor substrate 1 in which n-type region 4 is notformed so as to penetrate p-type region 3 and reach n⁻ region 2. Aninsulation film 11 formed of a silicon oxide film is formed so as tocover the inner wall surface of each of trenches 1 a and 1 b and thefirst main surface of semiconductor substrate 1.

A gate electrode 12 a serving as a control electrode is formed in trench1 a. Gate electrodes 12 a are formed so as to be opposed across p-typeregion 3 sandwiched between n⁻ region 2 and n-type region 4, andinsulation film (gate insulation film) 11. Thus, insulated gate fieldeffect part is formed of gate electrode 12 a, insulation film (gateinsulation film) 11, the n⁻ region 2, the n-type region 4, and p-typeregion 3.

Gate electrode 12 a is formed of a material having a conductive propertysuch as a polycrystalline silicon layer doped with an impurity (referredto as the doped polysilicon layer hereinafter), for example. Gateelectrode 12 a is formed only in trench 1 a and does not project fromtrench 1 a upward of the first main surface of semiconductor substrate1.

A potential fixing electrode 12 b is formed in trench 1 b. Potentialfixing electrode 12 b is formed of a material having a conductiveproperty such as the doped polysilicon layer, for example. Potentialfixing electrode 12 b has a part projecting from trench 1 b upward ofthe first main surface of semiconductor substrate 1 and this projectingpart has an expanding part expanding in the lateral direction (in thein-plane direction of the fist main surface) so as to have a width w2larger than the width w1 of trench 1 b. In addition, insulation film 11is positioned between the expanding part of potential fixing electrode12 b and semiconductor substrate 1.

An insulation film 13 formed of such as a silicon oxide film is formedon the first main surface of semiconductor substrate 1. Insulation film13 has a contact hole 13 a covering over gate electrode 12 a andexposing the whole upper surface of the expanding part of potentialfixing electrode 12 b and a part of the first main surface ofsemiconductor substrate 1. An insulation film 19 formed of a siliconoxide film is formed on insulation film 13. In addition, insulation film11 is positioned between insulation film 13 and semiconductor substrate1.

A main electrode serving as an emitter electrode (or a source electrode)is formed on insulation films 13 and 19 and on contact hole 13 a. Themain electrode is connected to the whole upper surface of the expandingpart of potential fixing electrode 12 b exposed from contact hole 13 aand electrically insulated from gate electrode 12 a by insulation films13 and 19.

The main electrode has silicide layers 14 b and 16, a high melting pointmetal layer 14 a, a barrier metal layer 15, and a conductive layer 17.Silicide layer 14 b is formed on the whole upper surface of theexpanding part of potential fixing electrode 12 b. Silicide layer 16 isformed on the surface of semiconductor substrate 1 exposed from contacthole 13 a. High melting point metal layer 14 a is formed on each ofinsulation films 11, 13 and 19. Barrier metal layer 15 is formed onsilicide layers 14 b and 16 and high melting point metal layer 14 a.Conductive layer 17 is formed on barrier metal layer 15.

Since high melting point metal layer 14 a is an unreacted titanium (Ti)layer at the time of forming silicide, it does not exist in many cases,and even when it exists, it is extremely thin. Silicide layers 14 b and16 are formed of titanium silicide (TiSi₂). Barrier metal layer 15 is ametal film or a metal compound film formed in order to prevent thereaction between semiconductor substrate 1 and conductive layer 17 andit is formed of titanium nitride (TiN) layer. Conductive layer 17 isformed of a material having a melting point lower than that of barriermetal layer 15 and a resistivity lower than those of high melting pointmetal layer 14 a and barrier metal layer 15. When the silicon contentratio of conductive layer 17 is higher than 1%, conductive layer 17hardly reacts with the substrate silicon, which is no problem but whenconductive layer 17 is formed of a material that hardly generatessilicon nodule, that is, an aluminum-silicon (AlSi) alloy containingless than 1% of silicon or pure aluminum in view of wire bondingcharacteristics that will be described below, it has a property that islikely to react with the silicon material of the substrate as comparedwith high melting point metal layer 14 a and barrier metal layer 15.

Next, a manufacturing method according to the present embodiment will bedescribed.

With reference to FIG. 2, p-type region 3 and n-type region 4 are formedon the first main surface of semiconductor substrate 1 having n⁻ region2. Then, trench 1 a penetrating both n-type region 4 and p-type region 3and reaching n⁻ region 2, and trench 1 b penetrating p-type region 3 inwhich n-type region 4 is not formed and reaching n⁻ region 2 are formedin the first main surface of semiconductor substrate 1. Insulation film11 is formed so as to cover the inner wall surface of trenches 1 a and 1b and the first main surface of semiconductor substrate 1. Insulationfilm 11 is a silicon oxide film formed by a thermal oxidation method, asilicon oxide film or a silicon nitride film formed by a CVD (ChemicalVapor Deposition) method, or combination of the above films.

With reference to FIG. 3, a conductive layer 12 formed of a dopedpolysilicon film, for example, is formed on the first main surface ofsemiconductor substrate 1 to fill trenches 1 a and 1 b. In order to thinconductive layer 12, whole conductive layer 12 is etched back as a wholein some cases.

With reference to FIG. 4, a photoresist 21 is applied by a generalphotoengraving technique and then exposed and developed. Thus, resistpattern 21 having a width larger than that of trench 1 b is formed ontrench 1 b.

With reference to FIG. 5, using resist pattern 21 as a mask, conductivelayer 12 is processed by dry etching. The dry etching is performed untilthe surface of insulation film 11 is exposed at least, wherebyconductive layer 12 is selectively removed and conductive layer 12 a intrench 1 a and conductive layer 12 b just under resist pattern 21remain.

Conductive layer 12 a remains only in trench 1 a, and the upper surfaceof conductive layer 12 a is retreated from the first main surface ofsemiconductor substrate 1 (that is, downward of the first main surfacein the drawing). The gate electrode is formed by conductive layer 12 a.

Conductive layer 12 b fills trench 1 b, and projects upward from trench1 b so as to be higher than the first main surface of semiconductorsubstrate 1 and the projecting part expands so that the width thereof islarger than that of trench 1 b. Thus, potential fixing electrode 12 b isformed by conductive layer 12 b.

Then, resist pattern 21 is removed by ashing or the like.

With reference to FIG. 6, insulation film 13 is formed so as to coverthe first main surface of semiconductor substrate 1. Insulation film 13may be any of PSG (Phospho Silicate Glass), BPSG (Boro-Phospho SilicateGlass), BP (Boro-Phospho)-TEOS (Tetra-Ethyl-Ortho-Silicate) siliconoxide film.

With reference to FIG. 7, insulation film 13 is reflowed by a heattreatment and an upper surface thereof is flattened. Then, in order toenhance adhesion with a photoengraving photoresist, insulation film 19formed of a silicon oxide film, for example, is formed by a low-pressureCVD method and the like. Then, a photoresist 22 is applied to insulationfilm 19.

Insulation film 19 is not necessarily formed, and photoresist 22 may bedirectly applied onto insulation film 13.

With reference to FIG. 8, photoresist 22 is exposed and developed by ageneral photoengraving technique and patterned into a predeterminedshape. Resist pattern 22 is patterned so as to cover gate electrode 12 aand open potential fixing electrode 12 b and a peripheral part thereof.

Using the resist pattern as a mask, insulation films 19 and 13 areprocessed by wet etching and then processed by dray etching. Thus,contact hole 13 a reaching the upper surface of the expanding part ofpotential fixing electrode 12 b and the surface of semiconductorsubstrate 1 is formed in insulation films 19 and 13. Then, resistpattern 22 is removed by ashing and the like.

Insulation films 19 and 13 may be processed only by dray etching or onlyby wet etching in forming contact hole 13 a.

With reference to FIG. 9, a heat treatment (reflowing) is performed toround the shape of the open end of contact hole 13 a of insulation films19 and 13.

With reference to FIG. 10, a high melting point metal 14 made oftitanium, for example, is formed so as to cover the whole surface.

With reference to FIG. 11, barrier metal layer 15 made of titaniumnitride (TiN), for example, is formed by a reactive sputtering method,for example. Then, high melting point metal 14 is processed by a RTA(Rapid Thermal Anneal) process such as lamp annealing through barriermetal layer 15. Thus, the high melting point metal of high melting pointmetal 14 reacts with the silicon of conductive layer 12 or semiconductorsubstrate 1 and silicide layers (TiSi₂) 14 b and 16 consisting of highmelting point metal and silicon are formed. That is, silicide layer 14 bis formed at the contact part between high melting point metal 14 andconductive layer 12 and silicide layer 16 is formed at the contact partbetween high melting point metal 14 and semiconductor substrate 1.

At this time, high melting point metal 14 on insulation films 11, 13 and19 does not react and remains as unreacted high melting point metallayer (titanium layer, for example) 14 a in some cases.

Thereafter, conductive layer 17 made of aluminum, for example, is formedon the whole surface, and heat treatment is performed to stabilizebarrier metal layer 15, conductive layer 17 and the like, whereby thesemiconductor device according to the present embodiment shown in FIG. 1is completed.

According to the present embodiment, since there is no gap generatedbetween potential fixing electrode 12 b and the inner wall surface oftrench 1 b, the semiconductor device can be highly reliable. This reasonwill be described hereinafter.

With reference to FIG. 12, in the case where potential fixing electrode12 b is formed only in trench 1 b, when contact hole 13 a is formed ininsulation film 13, insulation film 11 between potential fixingelectrode 12 b and the inner wall surface of trench 1 b is also etchedaway. In this case, an extremely small gap 50 is formed betweenpotential fixing electrode 12 b and the inner wall surface of trench 1b.

In addition, in a case where the high melting point metal to formsilicide layers 14 b and 16 by contact with silicon is formed bysputtering or the like, before being formed, the surface is etched awaywith fluorinated acid in order to remove a natural oxidation film at thesilicon exposed part. By such etching, insulation film 11 may be furtherdeeply etched.

It is extremely difficult to fill this extremely small gap 50 generatedas described above, with the high melting point metal and barrier metallayer 15. Further, even when the high melting point metal and barriermetal layer 15 are put on gap 50 so as to cover it, it is inevitablethat film thickness thereof becomes small and a pinhole is generated.

When an aluminum layer is formed as conductive layer 17 in this state,the aluminum of conductive layer 17 comes in contact with the silicon ofsemiconductor substrate 1 and the silicon of potential fixing electrode12 b directly, or conductive layer 17 is formed through the metal filmhaving a low barrier property. Thus, in this case, the silicon isdiffused in the aluminum and at the same time, the aluminum eats away inthe silicon as a spike (that is, an aluminum spike is generated), sothat the electric characteristics are considerably damaged and long-termreliability cannot maintained in some cases.

Meanwhile, according to the present embodiment, as shown in FIG. 1,potential fixing electrode 12 b has the expanding part expanding on thefirst main surface such that width w2 thereof is larger than width w1 oftrench 1 b. Thus, the expanding part of potential fixing electrode 12 bcovers insulation film 11 between the inner wall surface of trench 1 band potential fixing electrode 12 b. Therefore, at the time of etchingfor forming the contact hole shown in FIG. 8, insulation film 11 betweenthe inner wall surface of trench 1 b and potential fixing electrode 12 bcan be prevented from being etched away. Thus, since the extremely smallgap can be prevented from being generated, the barrier property of thebarrier metal does not deteriorate on this extremely small gap.Therefore, the aluminum of conductive layer 17 can be prevented fromreacting with the silicon of semiconductor substrate 1 and the siliconof potential fixing electrode 12 b, so that the semiconductor device canhave high reliability.

Since the whole upper surface of the expanding part of potential fixingelectrode 12 b is connected to the emitter electrode, the contact areabetween potential fixing electrode 12 b and the emitter electrode can belargely ensured. Thus, the potential of potential fixing electrode 12 bcan be fixed to the GND stably.

In addition, since the whole upper surface of the expanding part ofpotential fixing electrode 12 b is connected to the emitter electrode,processing precision required for forming contact hole 13 a shown inFIG. 8 does not need to be high.

If a contact hole is formed so as to reach only a part of the expandingpart of potential fixing electrode 12 b, the width of trench 1 b forpotential fixing electrode 12 b has to be larger than the width oftrench 1 a for the gate electrode. Thus, when trench 1 b and trench 1 aare formed at the same etching process, trench 1 b becomes deeper thantrench 1 a to some extent. As a result, electric field concentration isgenerated when a main withstand voltage is maintained during off time,which could cause the main withstand voltage to be lowered.

Meanwhile, according to the present embodiment, since the whole uppersurface of the expanding part of potential fixing electrode 12 b is incontact with the emitter electrode, the width of trench 1 b can be thesame as that of trench 1 a. Thus, the electric field concentration whenthe main withstand voltage is maintained as described above can beprevented, and the main withstand voltage can be highly maintained.

In addition, since potential fixing electrode 12 b is electricallyconnected with the emitter electrode and opposed to semiconductorsubstrate 1 across insulation film 11 to form a capacity, the potentialof semiconductor substrate 1 can be fixed and stabilized by potentialfixing electrode 12 b.

According to the present embodiment, potential fixing electrode 12 b iswoven in a place where millions or billions of cell groups arerepeatedly formed at the same pitch. Therefore, the semiconductor deviceaccording to the present embodiment is suitable for miniaturization ofthe cell dimension accompanied by high integration.

In addition, according to the present embodiment, even when theplurality of potential fixing electrode 12 b are adjacently formed,p-type region 3 sandwiched between adjacent potential fixing electrodes12 b can electrically in contact with the emitter electrode. Thus,p-type region 3 sandwiched between adjacent potential fixing electrodes12 b does not become a floating state electrically, so that it can besurely the ground potential.

As one example of the method of forming the laminated structure havingtitanium silicide (TiSi₂) layer 14 b and titanium nitride (TiN) layer 15as shown in FIG. 1, a titanium (Ti) layer formed on a silicon bysputtering is processed by lamp annealing so that titanium silicide isformed on the lower side of the titanium layer that is in contact withthe silicon and titanium nitride is formed on the upper side of thetitanium layer by reaction with nitrogen gas in the lamp annealingatmosphere. The titanium silicide layer on the lower side is provided toimprove ohmic characteristics, and the titanium nitride on the upperside becomes a barrier metal. According to the above method of formingthe titanium nitride layer by thermal nitridation using the lampannealing, since the thickness of the titanium layer is divided into thesilicide layer on the lower side and the titanium nitride layer on theupper side.

Thus, when the titanium nitride layer needs to be thick, it ispreferable that the titanium nitride layer is formed by a reactivesputtering method. When this method is used, a laminated structureconsisting of titanium silicide layer 14 b, reactive titanium nitridelayer 15, and aluminum material layer 17 is provided. Aluminum materiallayer 17 includes pure aluminum, an aluminum-silicon (AlSi) alloycontaining less than 1% of silicon, an aluminum-copper (AlCu) alloy, andan aluminum-silicon-copper (AlSiCu) alloy.

In the case of a bipolar IC (Integrated Circuit) and a power device, aplatinum silicide (PtSi) layer that is a silicide layer having morepreferable ohmic characteristics than titanium silicide is used as thesilicide layer in some cases. In this case, a laminated structureconsisting of the platinum silicide (PtSi) layer, a titanium tungsten(TiW) layer, and an aluminum material layer is used.

Embodiment 2

The constitution shown in FIG. 1 can be applied to a vertical type IGBTshown in FIGS. 13 to 15, a vertical type n-channel MOSFET (referred toas n-MOSFET hereinafter) shown in FIG. 16, and a lateral type IGBT shownin FIG. 17.

The vertical type means that a main current flows between electrodesformed on the first and second main surfaces of a semiconductorsubstrate. Further, the lateral type means that a main current flowsbetween electrodes formed on the first main surface of a semiconductorsubstrate.

With reference to FIG. 13, this constitution is in a case where theconstitution in FIG. 1 is applied to a vertical PT (Punch Through) typeIGBT. In this constitution, n⁺ region (n⁺ buffer region) 5 and a p⁺region (p⁺ collector region) 6 are sequentially formed on the secondmain surface side of n⁻ region (n⁻ drift region) 2 of semiconductorsubstrate 1. A main electrode (collector electrode) 18 is formed on thesecond main surface of semiconductor substrate 1 so as to be in contactwith p⁺ region (p⁺ collector region) 6.

Further, with reference to FIG. 14, this constitution is in a case wherethe constitution in FIG. 1 is applied to a vertical LPT (Light PunchThrough) type IGBT. In this constitution, n-type region (n-type bufferregion) 5 and p-type region (p-type collector region) 6 are sequentiallyformed on the second main surface side of n⁻ region (n⁻ drift region) 2of semiconductor substrate 1. Main electrode (collector electrode) 18 isformed on the second main surface of semiconductor substrate 1 so as tobe in contact with p-type region (p-type collector region) 6.

With reference to FIG. 15, this constitution is in a case where theconstitution in FIG. 1 is applied to a vertical NPT (Non Punch Through)type IGBT. In this constitution, p-type region (p-type collector region)6 is directly formed on the second main surface side of n⁻ region (n⁻drift region) 2 of semiconductor substrate 1. Main electrode (collectorelectrode) 18 is formed on the second main surface of semiconductorsubstrate 1 so as to be in contact with p-type region (p-type collectorregion) 6.

With reference to FIG. 16, in this constitution, n⁺ region (n⁺ drainregion) 5 is directly formed on the second main surface side of n⁻region (n⁻ drift region) 2 of semiconductor substrate 1. Main electrode(drain electrode) 18 is formed on the second main surface ofsemiconductor substrate 1 so as to be in contact with n⁺ region (n⁺drain region) 5.

With reference to FIG. 17, in this constitution, n-type region (n-typebuffer region) 5 is formed in n⁻ region (n⁻ drift region) 2 in the firstmain surface of semiconductor substrate 1. In addition, p-type region(p-type collector region) 6 is formed in n-type region (n-type bufferregion) 5 in the first main surface of semiconductor substrate 1.

A main electrode (collector electrode) region is formed on the firstmain surface so as to be in contact with p-type region (p-type collectorregion) 6. The main electrode (collector electrode) has silicide layer16 being in contact with p-type region (p-type collector region) 6,unreacted high melting point metal 14 a formed on insulation films 11,13, and 19, barrier metal layer 15 formed on silicide layer 16 and highmelting point metal 14 a, and conductive layer 18 formed of aluminum onbarrier metal layer 15 on the first main surface of semiconductorsubstrate 1.

The constitution of the lateral type IGBT shown in FIG. 17 can beobtained such that the constitution of the vertical PT type IGBT shownin FIG. 13 is made to be the lateral type. Similarly, the constitutionshown in FIG. 1 may be applied to the one in which the LPT type verticalIGBT shown in FIG. 14 is made to be the lateral type, and the one inwhich the NPT type vertical IGBT shown in FIG. 15 is made to be thelateral type.

Since the constitution other than the above in FIGS. 13 to 17 is almostthe same as that in Embodiment 1 shown in FIG. 1, the same signs areallotted to the same components and description thereof will not begiven.

Also in each of the constitutions shown in FIGS. 13 to 17, sincepotential fixing electrode 12 b has the expanding part on the first mainsurface so that width w2 thereof is larger than width w1 of trench 1 b,a gap is prevented from being generated between potential fixingelectrode 12 b and trench 1 b, so that the semiconductor device havinghigh reliability can be provided.

Embodiment 3

While the case where the gate of the insulated gate field effect parthas the trench gate structure has been described in Embodiment 1 shownin FIG. 1, the gate of the insulated gate field effect part may have aplanar gate structure. Hereinafter, the constitution will be described.

With reference to FIG. 18, n⁻ region 2 serving as a drift region, forexample, is formed in semiconductor substrate 1 formed of silicon.P-type region 3 serving as a base region, for example, is selectivelyformed on n⁻ region 2 on the first main surface side of semiconductorsubstrate 1. N-type region 4 serving as an emitter region (sourceregion), for example, is selectively formed in p-type region 3 on thefirst main surface side of semiconductor substrate 1.

On the first main surface, gate electrode 12 a is formed on p-typeregion 3 sandwiched between n-type region 4 and n⁻ region 2 throughinsulation film (gate insulation film) 11. Gate electrode 12 a is formedon the flat first main surface and not formed in a trench. Insulationfilm (gate electrode) 11 is formed of a silicon oxide film and gateelectrode 12 a is formed of a nonmetal material having a conductiveproperty such as a doped polysilicon layer.

An insulated gate field effect part is formed by gate electrode 12 a,insulation film (gate insulation film) 11, n⁻ region 2, n-type region 4,and p-type region 3.

Since the constitution other than the above in the present embodiment isalmost the same as that in Embodiment 1 shown in FIG. 1, the same signsare allotted to the same components and description thereof will not begiven.

Thus, even when the gate of the insulated gate field effect part has theplanar gate structure, since, similarly to Embodiment 1, potentialfixing electrode 12 b has an expanding part on the first main surface sothat a width thereof is larger than that of trench 1 b, a gap isprevented from being generated between potential fixing electrode 12 band the wall surface of trench 1 b, so that highly-reliablesemiconductor device can be provided.

The constitution of the present embodiment can be also applied to thevertical type IGBT shown in FIGS. 13 to 15 and the vertical type MOSFETshown in FIG. 16 and the lateral type IGBT shown in FIG. 17 similar tothe constitution of Embodiment 1.

Embodiment 4

While the IGBT and MOSFET have been described in Embodiments 1 to 3, thepresent invention can be applied to another element having an insulatedgate field effect part, and applied to a carrier storage type IGBT, MCT(MOS-Controlled Thyristor), IEGT (Injection Enhanced Gate Transistor)and the like. Hereinafter, their constitutions will be described.

With reference to FIG. 19, a carrier storage type IGBT according to thepresent embodiment is different from the PT type vertical IGBT shown inFIG. 13 in that an n-type CS (Carrier Stored) layer 31 is added betweenn⁻ region 2 and p-type region 3.

Since the constitution of the carrier storage type IGBT other than theabove is almost the same as the constitution shown in FIG. 13, the samesigns are allotted to the same components and description thereof willnot be given.

With reference to FIG. 20, according to an MCT in the presentembodiment, n⁻ region 2 serving as a drift region, for example, isformed in semiconductor substrate 1 formed of silicon, for example.P-type region 3 serving as a base region, for example, and an n-typeregion 32 serving as a cathode region, for example, are sequentiallyformed on n⁻ region 2 on the side of the first main surface ofsemiconductor substrate 1. A p⁺ region 33 serving as a short emitterregion, for example, is selectively formed in n-type region 32 on theside of the first main surface of semiconductor substrate 1.

Trench 1 a is formed in the first main surface of semiconductorsubstrate 1 so as to penetrate p⁺ region 33, n-type region 32 and p-typeregion 3 and reaching n⁻ region 2. In addition, trench 1 b is formed inthe first main surface of semiconductor substrate 1 in which p⁺ region33 is not formed is formed so as to penetrate n-type region 32 andp-type region 3 and reaching n⁻ region 2. Insulation film 11 formed of asilicon oxide film, for example, is formed so as to cover the inner wallsurface of each of trenches 1 a and 1 b and the first main surface ofsemiconductor substrate 1. Gate electrode 12 a is formed in trench 1 aand potential fixing electrode 12 b is formed in trench 1 b.

Since the constitution of the MCT other than the above is almost thesame as the constitution shown in FIG. 13, the same signs are allottedto the same components and description thereof will not be given.

With reference to FIG. 21, an IEGT according to the present embodimentis different from the PT type vertical IGBT shown in FIG. 13 in that agate thinning structure is added between gate electrode 12 a andpotential fixing electrode 12 b.

This gate thinning structure has at least two trenches 1 c, and dummygates 12 c filling trenches 1 c. Each of two trenches 1 c is formed inthe first main surface of semiconductor substrate 1 in which n-typeregion 4 is not formed so as to penetrate p-type region 3 and reach n⁻region 2. Insulation film 11 formed of a silicon oxide film is formed onthe inner wall of each of two trenches 1 c.

Each of two trenches 1 c is filled with dummy gate 12 c. Dummy gate 12 cfilling each of two trenches 1 c has an expanding part so that a widththereof is larger than the width of trench 1 c. The expanding parts ofadjacent dummy gates 12 c are connected on the first main surface ofsemiconductor substrate 1, whereby adjacent dummy gates 12 c have thesame potential. P-type region 3 sandwiched between two trenches 1 c isin an electrically floating state.

Insulation films 13 and 19 are formed so as to cover the expanding partsof two dummy gates 12 c. An emitter electrode is formed on insulationfilms 13 and 19.

The number and interval of dummy gates 12 c in the IEGT can be setarbitrarily according to the characteristics (main withstand voltagelevel, current density, operation speed and the like) and the structurerequired to the IEGT.

Since the constitution of the IEGT other than the above is almost thesame as the constitution shown in FIG. 13, the same signs are allottedto the same components and description thereof will not be given.

Thus, in any of the carrier storage type IGBT, MCT and IEGT, similar toEmbodiment 1, since potential fixing electrode 12 b has the expandingpart on the first main surface such that a width thereof is larger thanthe width of trench 1 b, a gap is prevented from being generated betweenpotential fixing electrode 12 b and the wall surface of trench 1 b,whereby a highly-reliable semiconductor device can be provided.

(Other)

Another example with a different shape of an emitter region will bedescribed.

FIGS. 22A and 22B show an example in which the shape of the emitterregion is changed, in which FIG. 22A is a schematic plan view showingthe electric connection between an emitter electrode and the emitterregion, and FIG. 22B is a schematic sectional view taken along lineXXIIB-XXIIB in FIG. 22A. With reference to FIG. 22A, n-type region(emitter region) 4 and p-type region (base region) 3 are arranged in theshape of stripe in the direction intersecting (at right angle, forexample) with the extending direction of trenches 1 a and 1 b on thefirst main surface of semiconductor substrate 1. That is, as shown bythick lines in FIG. 22A, n-type region (emitter region) 4 is formed inthe shape of a band although it is divided by trenches 1 a and 1 b in aplan view. In addition, p-type region (base region) 3 is also formed inthe shape of a band although it is divided by trenches 1 a and 1 b inthe plan view.

Thus, n-type region (emitter region) 4 and p-type region (base region) 3are formed in a band shape on the first main surface alternately in planview, and the band-shaped region of n-type region (emitter region) 4 isformed of n-type region (emitter region) 4 only except for trenches 1 aand 1 b, and the band-shaped region of p-type region (base region) 3 isformed of p-type region (emitter region) 3 only except for trenches 1 aand 1 b.

Since n-type region (emitter region) 4 and p-type region (base region) 3are arranged in a stripe shape, silicide layer 16 is in contact withboth n-type region (emitter region) 4 and p-type region (base region) 3.Therefore, according to the emitter electrode, silicide layer 16 iselectrically in contact with both n-type region (emitter region) 4 andp-type region (base region) 3.

While description has been made for the case where the material ofsemiconductor substrate 1 is silicon in the above embodiments, thematerial of semiconductor substrate 1 according to the present inventionis not limited to the silicon material and it may be a semiconductormaterial other than silicon or a semiconductor material formed of acompound of silicon and another element. For example, the material ofsemiconductor substrate 1 includes a wide band gap material such assilicon carbide (SiC) or gallium nitride (GaN), or a compoundsemiconductor material such as silicon germanium (SiGe), gallium arsenic(GaAs), indium phosphorus (InP), or gallium aluminum arsenic (GaAlAs),or a II-VI compound semiconductor material such as diamond, pyloriticgraphite, p-BN (Pyloritic Boron Nitride), cadmium sulfide (CdS), orcadmium selenium that is a wide band gap semiconductor material formedof carbon element.

The present invention can be especially advantageously applied to apower semiconductor device.

The conductivity types (p-type and n-type) shown in the aboveembodiments may be reversed.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the scopeof the present invention being interpreted by the terms of the appendedclaims.

1. A semiconductor device comprising: a semiconductor substrate having afirst main surface and a trench in said first main surface; an elementhaving an insulated gate field effect part including a gate electrodeformed in said first main surface; a potential fixing electrode fillingsaid trench and having an expanding part on said first main surface sothat a width of the expanding part is larger than that of said trench;and a first main electrode formed on said first main surface,electrically insulated from said gate electrode, and connected to anupper surface of said expanding part of said potential fixing electrode,said first main electrode comprising first metal films and a secondmetal film formed on said first metal films, said second metal filmhaving a melting point lower than that of said first metal films, andsaid second metal film is formed of a material which more readily reactswith a material of said semiconductor substrate than a material of saidfirst metal films.
 2. The semiconductor device according to claim 1,wherein said element is a bipolar transistor having said insulated gatefield effect part.
 3. The semiconductor device according to claim 1,wherein said semiconductor substrate has a second main surface opposedto said first main surface, said semiconductor device further comprisesa second main electrode formed on said second main surface, and saidelement is a vertical type element in which a main current flows betweensaid first main electrode and said second main electrode.
 4. Thesemiconductor device according to claim 1, wherein said second metalfilm is not in direct contact with the expanding part of the potentialfixing electrode.